1. Field of the Invention
This invention relates generally to system and method for the mitigation of paraffin was deposition from crude oil and, more particularly, the invention relates to a system and method for the mitigation of paraffin wax deposition from crude oil by using ultrasonic waves.
2. Description of the Prior Art
Wax deposition from crude oil is an enormously expensive problem for oil producers around the world. In the field, the production tubing is often plugged by paraffin wax which deposits on the walls of the production tubing and surface flow equipment. The deposition of the paraffin leads to a fall in the production rates of the oil from that well.
The deposition of the paraffin waxes from the reservoir fluid occurs when the temperature and pressure move below the cloud point of the fluid. The paraffin deposits start off as a thin film and slowly deposits in the form of crystalline solids, which collects on the interior of the tubing and flow-lines and slowly chokes off the production.
Basically, paraffin deposits are carbonaceous material, which is not soluble or dispersible by the crude oil under the prevailing conditions. Paraffins are composed primarily of alkanes with formulas C18H38 to C70H172. These are straight chained and branch chained compounds, and are generally inert and resistant to attack by acids, bases, and oxidizing agents. Previous research has shown that n-paraffins are more responsible for this problem. The formation of the deposit depends on the cloud point, an available surface and or loss of gas or light ends due to a drop in pressure. The precipitation is not uniform; it has peaks at certain points in the tubing and less deposition at other places.
The cloud point temperature is the key factor controlling the paraffin wax deposition. Paraffinic hydrocarbon liquids form a paraffin or wax solid phase when the temperature falls below the cloud point, or Wax Appearance Temperature (WAT), of the oil. As the oil flows up the well-bore, its pressure drops causing solution gas to liberate. This solution gas which is liberated acts to some degree as a solvent for waxes. Therefore, the loss of gas increases the cloud point temperature causing more precipitation and also makes the oil more viscous.
Also, as the oil moves upward, it cools since the ground temperature is less than the reservoir temperature. There is a temperature gradient at the wall and when the oil temperature reaches the cloud point the precipitation starts. This precipitation occurs even if the bulk oil temperature is more than the cloud point temperature, because it is the temperature of the oil at the wall, which plays the most important role in the precipitation of wax. The wax deposition problem is more prevalent in low flow rate wells because of the high residence time of oil in the well-bore. The increased flow time leads to more heat loss, which results in lowering of oil temperature and leads to wax precipitation and deposition. Well-bore studies have shown that the temperature profile in the well-bore is a strong function of the flow-rate. The paraffin wax problem is an example of fluid/solid equilibrium, which is described as a solution of higher molecular weight hydrocarbons in low molecular weight hydrocarbons which act as solvents.